[Config] Add type-safe configuration parsing

[Config] Add type-safe configuration parsing

This makes the GKeyFile engine do the parsing for all of the GObject
properties, instead of rolling our own. The default configuration was
moved to a file (share-tilda.conf) which will live in /usr/share when
the project is autoconfed.

The rewritten configuration parser determines the type of parameter
given to it using its type registration, then invokes the appropriate
parser in GKeyFile. The whole thing is basically function overloading
from C++, but done in C.

I also exported all of the enums to the tilda-types.[ch] files, then
hooked them into the GType system so they can be auto-parsed later.
The config file parser is actually pretty nice, because it allows
you to use the enum value's nick in the configuration file. It's
harder for us as programmers (and harder on the computer) but it sure
makes for a pretty configuration file. Might as well make the computer
work /for/ us after all. ^_^

Sorry about the huge changeset.